A subsea intervention operation on a hydrocarbon comprising well typically includes:
Well Control Package (“WCP”)—typically comprising two subsea modules, Emergency Disconnect Package (“EDP”) and Lower Riser Package (“LRP”), typically surrounding the well bore with safety valves,
Riser System—a set of connected riser joints, typically pipes with approximate lengths 30-50 m, which connect the WCP and Workover rig or vessel,
Workover Control System (“WOCS”)—typically comprising electric, electronic and hydraulic systems that control practically all operations in WOS, said operations include, opening and closing of valves, measuring of parameters including, temperature and pressure, energy supply to various equipment including, electric and hydraulic.
Nowadays there are increased requirements for the Safety Instrumented Systems (“SISs”), for example, the Norwegian Petroleum Authority requires stringent implementation of SISs to mitigate risks to personnel, environment and assets. In the Workover business segment, this mainly relates to three safety functions,
Production Shutdown (“PSD”),
Emergency Shutdown (“ESD”), and
Emergency Quick Disconnect (“EQD”).
The above functions strive to protect the rig or vessel from hazardous conditions such as hydrocarbon spill or leakage in the process area or environment, and spill from the riser. These functions further protect the integrity of the well, for example in the event of position loss. Position loss may occur for example, if the vessel/rig drifts outside a given area from the location of the well.
Implementation of the minimum scope of the safety functions is usually regulated through international standards such as IEC61508 and ISO 13628-7, where the latter also includes some Workover specific requirements.
U.S. Pat. No. 4,174,000 describes a method and apparatus for interfacing a plurality of control systems for a subsea well.
US2005/0121188A1 describes controlling a fluid well.
WO2011/041550A2 describes a subsea control system with interchangeable mandrel.
US2014/0374114A1 describes a subsea intervention system.